1. Field of Invention
This invention pertains to a circuit for generating a reset pulse after a power supply for an electronic system has been energized, and more particularly to a miniaturized circuit which could be incorporated into a large-scale integration (LSI)-type chip.
2. Description of the Prior Art
In many electronic circuits, certain components are used which can have two or more stable states. For example, digital circuits often comprise flip-flops, latches and counters. These types of components must be set to an initial or reset state prior to their normal operation every time the circuit is energized. Typically one or more circuits are energized from a single power supply. However as a power supply is activated, its output rises in an unpredictable manner with frequent fluctuations prior to reaching a final nominal steady state value. This is especially the case with switched power supplies in which oscillators and SCR's are used to convert a (usually high) D.C. or A.C. voltage and a (usually low) D.C. voltage. Because of this initial variation in the power supply output it is very difficult to insure that the above-mentioned multistate components are in a particular state after the power supply output has stabilized. Therefore an initializing, or a reset pulse is needed to set said components to the desired states. Normally the circuit used to generate this reset pulse is activated only once, for each power-up operation, and is left inactivated at all other times. It has been found that the reset pulse must have a duration, which depending on different power supplies ranges from microseconds to seconds.
In order to conserve space, and power and increase the operational speed of the electronic circuits, these circuits have been miniaturized by using well-known I.C. techniques such as CMOS. However reset pulse-generating circuits traditionally comprised passive elements such as resistors and capacitors which cannot be implemented on CMOS IC and therefore must be mounted externally.